Trick or Treat
by KaeCooks
Summary: Set 16 months after "A Little Extra." Established Casett. The members of 51 plan a Halloween party. Casey decides to give them more of a reason to celebrate.
1. Chapter 1

**Disclaimer: Nothing here is mine except the plot. **

**Set 16 months after ALE. (October 2021) Established Casett/Brettsey.**

* * *

The Monday before Halloween, the firefighters and paramedics of Firehouse 51 were sitting around, eating breakfast during the last few hours of their shift.

"Herrmann!" Kidd exclaimed. "We should totally do a costume night at Molly's. "

"I'm listenin'," Herrmann replied.

"We could do a competition. Anybody who comes dressed up for Halloween gets ten percent off drinks. We could do a cash prize for best costume."

"And who's gonna do all the decorating for this?" he asked.

Brett and Foster chimed in, "Girl, we got you."

Kidd smiled. "The three of us ladies will take care of it, Herrmann."

"Then it's settled!" Herrmann exclaimed. "Halloween night at Molly's!"

With that, the common room erupted into a buzz of costume and decoration planning until the next shift filtered in and everybody went their separate ways.

* * *

Sylvie collapsed on the couch when they got home. Matt grabbed two bottles of water from the kitchen. He lifted Sylvie's legs from the couch so he could sit beside her. He handed off one of the bottles and set Sylvie's legs down on his lap.

"So," she asked, taking a sip of water, "Do you want to do a couple's costume? Or should we do separate costumes?"

"Hmmm, we're a couple?" Matt asked facetiously, his mind flicking to a certain errand he'd dragged Stella on some three weeks prior while Foster was distracting Sylvie.

"Matthew Casey," Sylvie chastized, playfully swatting his chest.

"What?" he asked, playing coy.

"I think I might need to give you a thorough examination," she purred, grabbing his glass and setting it on an end table beside hers before crawling onto his lap. "If you can't remember that we've been together for over a year and a half, you have something _seriously_ wrong."

"Oh? And what exactly would this examination entail?" he asked, nuzzling into her neck.

She could already feel his member straining against his jeans. "Let's get you into a bed and I'll show you."

He moaned as she rocked her hips against him. Not wanting to wait any longer, he wrapped his arms tightly around her and stood. She wrapped her legs around his waist and started kissing where his neck met his shoulders. He dropped her onto the bed and they wasted no time ridding each other of their clothes.

* * *

After lunch that afternoon, they were washing dishes together.

"When are you meeting Kidd and Foster to decorate Molly's?" Matt asked.

"Umm, we haven't really discussed it yet," Sylvie replied. "Why?"

He shrugged. "I was just thinking how it's been a while since just the two of us went out somewhere. Since we're probably going to have to do some degree of shopping for costumes, I thought maybe we could do it then."

Sylvie smiled at him. "Sounds fun to me," she said. "That means we'll have to figure out what we're going to do soon."

"Well, Sylvie-bean, did you have any ideas?"

Putting the last of the dishes away, she replied, "Nothing fantastic off the top of my head. You?"

"I've got a great idea," he said. "We could be a paramedic and a firefighter! They'd love it."

Sylvie tsked and shook her head at him. "What am I going to do with you?"

He shrugged. "Tolerate me? Kick me to the curb? Marry me?" The last question kind of slipped, but he tried to keep his cool. He really wanted to surprise her. He just didn't have a good plan yet.

Much to his relief, she didn't seem phased by it. She laughed. "That's quite the range of options, darling. I guess I'll just have to keep you around for further consideration. . . at least for the time being."

He smiled at her. "Okay, so what can we come up with?"

She thought about it for a minute. "We could be Bonnie and Clyde."

"I feel like that would require a shotgun as part of the costume."

"You're not wrong. Probably best to avoid that, then."

"Do you think we could pull off dressing up like Severide and Kidd?"

"Only if we got them to dress up like you and me. Danny and Sandy from _Grease?_"

"Too much hair product. Lucy and Ricky?"

"Eh. _I Love Lucy_ was funny, but I feel like we'd be expected to imitate their voices, and that would be a lot of strain on my vocal folds."

"Fair enough."

The suggestions died down for a couple minutes as they racked their brains for more ideas.

Suddenly, Sylvie gasped. "I've got it!"

"Do tell."

"Fred and Daphne from _Scooby Doo._"

"We have a winner," Matt said. It was too perfect.

Sylvie beamed. They decided to go shopping the following day. She was beyond excited and started rattling off a list of what they would need for their costumes, thinking through what they already had in their wardrobes.

Matt's mind was suddenly spinning. He had less than 24 hours to come up with the perfect plan. Sure, he'd been sitting on it for two weeks since the ring came in, but he was nervous. What was he going to do? Where was he going to take her? How was he going to ask her?

"Matt?" Sylvie's voice cut through his inner turmoil. "Matt, baby, you look like you've seen a ghost."

Trying to make a quick recovery, he blurted, "Zoinks!"

"And here I thought you were going to be Fred, Shaggy."

"Sorry," he said. "I just spaced out there for a minute."

"I could tell. Is everything okay?"

"Um, yeah." The apartment was suddenly too small. He quickly changed the subject and the two planned out what they were going to do the next day.

* * *

After a full morning shopping, getting groceries, and going out for a nice lunch at a local diner, Matt and Sylvie collapsed on the couch. All of a sudden, Matt came up with an idea.

"You know what I think?" he asked before he had time to talk himself out of it.

Sylvie looked up from where she had cuddled into his chest. "Hmm?"

"We should practice trick or treating that way we're ready for trick or treaters."

Sylvie looked at him, brows furrowed in a question, but she decided to play along. "Okay. . . "

"We can pretend the bedroom door is the front door. You be the trick or treater first. Give me one minute to get ready."

"You're on the clock, mister," she said playfully. She had no idea why he was acting so strange the last couple days, but if his most recent suggestion involved any bedroom activities, she would happily play along.

Matt disappeared to the bedroom and shut the door behind him. He quickly rummaged through his sock drawer and grabbed the small box that had been hidden there for two weeks. He held it behind his back and went to the door, just as Sylvie knocked. He opened the door.

"Trick or treat!" She said.

"Which would you prefer?"

Sylvie chuckled. What was he up to? "A treat, of course."

Matt dropped to one knee and pulled his hand out from behind his back.

Sylvie gasped. _That_ is why he seemed so preoccupied. "Oh my goodness." Was this really happening?

"Sylvie Brett, you are my rock, my sounding board, my best friend, and my better half. You've celebrated with me during some of the best moments of my life, and you've supported me through some of the worst. I don't know where I would be without you, so I always want to be with you. Will you do me the honor of becoming my wife?"

Sylvie was smiling and laughing and crying all at once. Words were too hard to summon, so she just nodded enthusiastically and kneeled, pulling his face to hers. Their lips came crashing together. When they finally broke for air, she held his face in her hands. "Matthew Casey," she said, "Nothing would make me happier." He slid the ring onto her finger and pulled her into a crushing embrace. They couldn't wait to spend forever together.


	2. Chapter 2

**Disclaimer: disclaimed.**

* * *

"So," Matt asked on their drive to work the next morning, "do you want to give a formal announcement or just see how it plays out?"

Sylvie thought about it for a moment. "Waiting would be fun, but I'm leaning toward a formal announcement. What do you want to do?"

"Let's see if we can keep it hidden just until everyone gets there. Then we can tell everyone at once."

"Sounds perfect," Sylvie said, throwing a smile at her fiance.

"You're perfect," he said back.

Sylvie's heart melted. "So are you. I can't wait to marry you."

"Wanna grab a flight to Vegas after shift?" he joked.

Sylvie laughed. "As fun as that would be, I think I'd prefer a bit more planning."

"Me too."

They found a spot to park and got out. Sylvie made a conscious effort to shove her left hand in her pocket. It would have to stay there until they made sure everyone had arrived for their news.

* * *

Half an hour later, everyone had gathered in the common room for breakfast. Casey, Severide, and Boden strolled in after their meeting. Matt walked over to Sylvie and put his hands on her shoulders. "Ready?" he whispered in her ear.

She nodded and stood up beside him.

Matt cleared his throat and spoke up, "Everyone, we have an announcement to make." All heads turned toward them and Sylvie pulled her hand out of her pocket for the first time since they'd arrived at the firehouse. "Brett and I are getting married."

The common room erupted in a chorus of congratulations with a three comments of, "It's about damn time." from Severide, Kidd, and Foster. Hugs and handshakes and friendly smacks on the back were given all around before everyone went back to their breakfast.

Kidd and Foster moved so they were sitting closer to Brett. "We have to know," Foster started.

"How did he ask you?" Kidd finished for her.

"Was it super romantic?" Foster questioned.

"Please tell me it was good. The man's been sitting on this thing for like a month."

Brett almost choked on the bite she'd just swallowed. "A month?"

"Girl, you remember that weekend you and I went that shopping spree out of town and this one," Foster said, jerking her head toward Kidd, "said she couldn't come because of something she and her boy toy were doing?"

Realization dawned on Sylvie's face. "You lied!" she exclaimed, lightly smacking Stella's shoulder.

"Casey cornered the two of us and asked for our help. We figured it would be easiest for Emily to distract you, and Kelly and I could go with Casey."

"Obviously, it worked. I just can't believe Matt managed to hide something from me for a whole month!" Sylvie said.

"Okay, now you gotta tell us. How'd he do it?" Stella refocused their conversation to the initial question.

All smiles, Brett told her friends the details of Casey's proposal, and the three chatted excitedly until the bells went off and they went to do their jobs.

* * *

After they got off work Halloween morning, Brett, Kidd, and Foster went straight to Molly's to set up for the party that night. They looped orange and black streamers across the ceiling. Fake spider webs were fastened in corners and above the bathroom stalls, complete with plastic spiders. The front door was wrapped in caution tape, and more was hung in front of the kitchen doors. Stella had found a stuffed witch that she propped against the bar. Emily brought a black cat that she set on the bar beside the witch. Sylvie improvised a cauldron with a big bowl she found in the back. She wrapped it in a black trash bag, set it on a stool in front of the witch, and sewed one of the witch's hands around a big stirring spoon. There was a Frankenstein cut-out beside the beer cooler, and a zombie cut-out outside the hallway to the bathrooms. Plastic jack-o-lanterns were scattered about. Around noon, the trio stepped back to take a look at their work.

"Looks good, ladies," Stella said.

"We dominated this place," Emily commented.

"There's just one more thing," Sylvie said, "but tell me what you guys think."

Foster and Kidd exchanged questioning looks while Brett ran to get something out of her car. Sylvie came back in and set up a picture frame on the bar near the wall. She strung an eye patch over it and propped a pirate hat on top. When she stepped back, the other two saw it was a picture of Otis.

"It's hard to believe it's been over two years," Stella said somberly.

"I wish I could have gotten to know him better," Foster lamented.

"I still miss him," Sylvie sighed, "but I thought, this way, it'd kinda be like he was here with us."

"It's perfect," Stella said.

With that, the trio went to their respective homes to get themselves rested and ready for the party that night.

* * *

A few hours later, costumed couples and singles started filtering in to Molly's. Herrmann lead the parade in a banana suit. Boden and Donna were close behind, dressed as Fred and Wilma Flintstone. They didn't come often, focusing mainly on spending time with Terrence, but it was still fun whenever they showed up.

Casey and Brett as Fred and Daphne pulled in with Foster, who was rocking a Cruela Du Vil costume, and Severide and Kidd, who decided to dress up as a koala bear and a tree. If anything, it gave Stella more of an excuse to cuddle up to her boyfriend.

Trudy and Mouch walked in their faces framed as Susan and Bill from the game Guess Who. Capp and Tony strode through the door in their Blackhawks gear. Cruz and Chloe came as a peanut butter and jelly sandwich. Gallo and Violet with Ritter and his boyfriend finished the parade as Soap and a loofa, and The Cowardly Lion and Tin Man, respectively.

Over the course of the night, people cast votes for whose costume they thought was best. Drinks were had, everyone encourraged by the 10% they saved by wearing costumes, albeit Capp and Tony had to convince a skeptical banana (Herrmann) that they were, in fact, in costume.

At nine thirty, Herrmann got Kidd, Brett, and Foster to come count the votes. Around ten o'clock, they'd finished, and Stella called for everyone's attention. "Alright, everybody, listen up!" she yelled, then gave the crowd a moment to settle down. "We have the winner of the costume contest. In third place, we have a tie: Blake Gallo and Violet with Joe Cruz and Chloe!" she paused for a round of applause.

When the clapping died down, Foster announced, "In second place: Severide and Kidd!"

Another round of applause sounded, then Brett spoke up, "And the winner of Molly's costume contest is," she paused as everyone hit the tables or bar for a drumroll, "Chief Boden and Donna!"

A final cheer erupted as Boden and Donna bowed and went to collect their prize. They said their thanks, then left to relieve their sitter. A few others filtered out behind them, but most people stayed until closer to closing time before going home.

* * *

At nearly three in the morning, Matt was helping a very drunk Sylvie Brett into their apartment. They were barely through the door when Sylvie slurred, "Maaatt, I hade clofes. Why ammi wearing dem?"

Matt just chuckled and led her to the bedroom as she started lazily grabbing at small accessories and dropping them on the floor. When they crossed the threshold of the bedroom, her face lit up a little and she clumsily vaulted herself onto the bed. She mumbled, "Ibe mished dis," and fell asleep almost immediately.

Shaking his head, Matt carefully maneuvered his fiance, getting her out of her costume. He grabbed one of his button down shirts and slipped it on her, buttoning it up, then tucking her in on her side of the bed. Once he had her situated, he slipped out to the kitchen to grab a bottle of water and aspirin. He came back to the bedroom and set them both on the nightstand on Sylvie's side before he stripped out of his costume and got into bed in just his boxers, then he, too, was soon asleep.

* * *

Sylvie woke up the next morning with a pounding headache. She had definitely drunk too much the night before. The first thing she saw was the bottle of water and the aspirin. She popped a couple aspirin and downed almost the entire bottle of water. Not yet ready to get up, she rolled over and fell back asleep for another hour.

* * *

When she woke up again, her headache had subsided a little. She reached for the bottle of water she'd opened earlier, and noticed that a second had joined it. She finished off the first then twisted open the second. She grinned a little, knowing Matt had put everything there. She loved his sweet gestures. He took such good care of her. She let her mind wander, picturing how he might care for children someday. Her bladder shook her out of her reverie, and she chastized herself, _Don't get ahead of yourself, Sylvie._ _Someday. Not yet._ Grudgingly, she got up to use the restroom.

Finishing that business, she grabbed the two bottles and the aspirin off her nightstand and brought them to the kitchen, where she found Matt making chicken sandwiches. She filled the empty water bottle from the filter and put it back in the fridge, then walked behind Matt and wrapped her arms around him.

"Thanks for that," she said, referring to the aspirin and water.

"Anything for you," he replied, glancing over his shoulder.

Sylvie let him go and leaned herself up against the counter.

Matt finished putting the sandwiches together, then washed his hands. As soon as they were dry, he asked, "You hungry?"

Sylvie grinned. "A bit."

Jerking his head at the sandwiches, Matt said, "After you."

Sylvie smiled and pushed off of the counter, grabbing a plate and her water bottle and moving to the dining room. He was close behind her. They ate their meal, making small conversation about the night before and whatever else came to mind. It was so domestic, but so comfortable, so natural. They loved the simplicity of it, and they were excited to spend the rest of their lives doing this.

* * *

**A/N: Thanks so much for reading! Though this is the end of this fic, there's more to come for these two! As always, let me know what you think!**


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